You need a Vex Mind to help you read the map of the Infinite Forest. Head to Nessus to find one.
It's now or never. Enter the Infinite Forest and defeat Panoptes now, before the Vex future victory becomes inevitable.
A Deadly Trial
Brother Vance says there's a Temple of Osiris in the EDZ where you can revive Sagira.
Osiris's damaged Ghost appeared on Mercury—along with a Vex army. That can't be a coincidence.